Telephone-exchange system.



No. 793,971. PATENTED JULY 4, 1905. H. G. WEBSTER. TELEPHONE EXCHANGE SYSTEM'.

APPLIOATION FILED APR. 17, 1903.

`with the same line.

lliliyirniu trames Patented July 4.-, lQ,

lamenti lTFliCl@ SPECIFXGATIQNforming part of Letters Patent No. 793,971, dated July 4C, 1905,

Application iiled April 17, 1903. Serial Noy 153,085.

lle it known that l, llamar (Il. VVnns'rnn, a citizen oi' the United States, residing at (lhicago, in the county ot' (look and State ot" lllinois, have invented a certain new and useful improvement in Telephone-Exchange Systems, ot which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawing', Vforming a part ol" this specilication.

My invention relates to telephone-exchange systems, and more particularly to the so-called i test-circuit lor use in connection with multiple-exchange switchboards.

My invention is particularly well adapted Afor use in connection with telephone systems in which a source ol" current located at the central exchange is used for the purpose oi' supirilying talking and signaling currents to the subscriber-s substation apparatus.

lt has been the common practice to provide each line connected with a multiple-switchboard exchange with a plurality oiI spring'- jaclis, one lor each section ot' the multipleswitchboard. Test contacts or thimbles et' the jacks associated with any one line have been so connected with the circuits ol the system that the insertion ot' the plug oil an operators cord-circuit at any one et' the operators positions causes some change in the potential valueof the test-thimbles associated A, test-contact, which has usually been the ti p-contact oli' the ope-rators plug, when applied to a test-thimble ot' a busy line has caused the closure of an electrical circuit or caused the charge or discharge oi" a condenser, thereby producing a click in the operators telephol'le-receiver to indicate the busy condition of the tested line. Under normal conditions, in which the tested line is not in use, the associated test-thimbles are lt the purpose ol my invention to provide means whereby the potential ot' the test- 50 contact of an o} )erato1"s plug is made only slightly diiierent from that of the test-thimble of a busy line. The test thimblcs ot a line which is not in use are preferably insulated lrom the remainder ot the system, where- 5 5 by the application ol the ti p-contact of the testing-plug does not atleet the operators telephone set to cause a busy-test signal.

ln a common battery system, which l shall hereinafter more `fully describe, l l'iiid it desir- 6o able to secure the desired potential of the testing-tip contact by connecting this contact to an intermediate point or element between the terminals ot the common battery or other source olI current used in operating' the tele- 6 5 phone system.

My invention is closely allied with that dcscribed and claimed in my copending application, Serial No. M9559, filed March 25, 1903.

While my invention may be applied to a great variety olI telephone systems, l shall describe it as applied to a differential relay system, such as that illustrated inthe accompan ying drawing.

At each oli' the substations A and B, l. have illustrated the usual Form ol apparatus in which a receiver-hook l when in its normaldepressed position, due to the weight of the receiver 2, connects between the line-limbs 3 and it the 30 call-bell 5 and the condenser 6. Wllen in its upper position, due to the removal of the rcceiver 2, the switch-hook l, closes the circuit between the line-limbs 3 and fl through the transmitter 7 and the primary 8 oil an indue- 85 tion-coil whose secondary S) is serially connected with the receiver E2.

The line-limb 3, extending to each oiz the substations, leads to the central station C, where it is connected with the grounded positive terminal of the common battery l() through a winding ll oi the ditlerential cutott relay l2. The limb a ol. each ol. the telephone-lines is normally connected, through a line-signal and the winding la ot the diitferential cut-oliA relay, with the negative pole nently connected with thc limb 3 of the telephone-line, as shown. rl`he sleeve-contacts 18, as will be hereinafter more fully explained, also form the test-thimbles of the spring-jacls- The operators cord-circuit comprises an answering-plug 21 and a calling-plug 2s, whose tip-contacts are connected through the tip-strand 23 and whose sleeve-contacts areconnected by the sleeve-strand 24. The usual operators ringing and listening key 25 is provided, the manipulation of this key in one direction serving' to connect the operators telephone set 26 in bridge of the cord-strands. The manipulation of this key, in addition to connecting the operators telephone set in bridge of the cord-circuit, also serves to break the conductive continuity of the tip-strand, the condenser 27 being then included in the tip-strand circuit.

The sleeve-strand includes in its circuit the supervisory relays 28 and 29, which are respectively shunted by condensers 30 and 31. The common terminal of the supervisory relays is connected, through an impedance-coil 32, with the negative pole of the common battery 10. The armatures 33 and 34E directly control the continuity of circuits through the supervisory signal-lamps 35 and 36, the operation ot' these lamps being dependent upon the connection with the contact 3T of the armature 38 of the supervisory controlling-relay 39, which is connected between the negative pole 'of the battery 10 and the tip-strand 23 of the operators cord-circuit.

A manipulation oi' the ringing-key serves to connect the calling-generator l0 in bridge of the cord-circuit. A conductor 41 then serves to connect the tip-strand 23, leading to the calling-plug 22, with the negative pole of the battery 10. A condenser L12 is included in the operators telephone-circuit. A conductor 43 connects the upper contact of the listening-hey 25, through an impedance-coil 4A, with a point L15 intermediate between the end terminals of the common battery 10.

rlhe operation of the system described is as follows: The removal of the receiver at sub station A from its switch-hook 1 causes the closure of a circuit from the battery 10 through the line-relay 13 and the two differential windings of the cut-ofi' relay 12. On account of the diierential relation of these windings ot' the cut-ofi' relay no net energization thereof is produced and its armature 15 is therefore not attracted. The line-relay 13 being energized, however, causes the actuation of a visual signal, which the operator answers by the insertion of the plug 21 of her cord connecting apparatus within one ot the line-jacks associated with the line leading to substation A. The insertion of this plug within a jack, as shown, causes the closure of a circuit, which may be traced as follows: from the negative pole oi' the battery 10, through the supervisory controlling-relay 39, the tip-strandot1 the cord connecting apparatus, the tip-contact of the plug 21, the tip-spring 2O of the line-jack, the winding 11 of the diierential cut-off relay 12, to the positive pole of the battery 10. The closure of this circuit of decreased resistance through the winding 11 of the differential cut-off relay causes a net energization thereof, whereupon its armature 15 is attracted into the position shown. rlhe attraction ot' this armature causes a break in the otherwise continuous circuit from the negative pole of the battery 10, through the line-relay and the winding 1-1 of the differential cut-oft' relay, to the substation A. At the same time the attraction of the armature 15 connects the line-limb 11, leading to the calling substation, directly with the sleeve-springs and test-thimbles 18 of the associated line-jacks 19. A circuit from the battery 10 may now be traced through the substation-transmitter as follows: from the positive pole ot' the battery 10, through the winding 11 of the differential cut-off relay, through theline-limb 3, switchhook 1, primary winding 8, transmitter T, line-limb L1, armature 15, contact 17, sleevespring 13, strand 24 of the cord-circuit, the winding of the supervisory relay 28, and the impedance-coil 32, to the negative pole of the battery 10. The closure of this circuit causes the attraction of the armature 33 of the supervisory relay 28, whereupon the otherwise completed local circuit through the supervisory signal-lamp 35 is broken. Upon the insertion of the answeringplug 21 within a linejack 19 a circuit is established through the supervisory signal-lamp 36 on account of the attraction of the armature 38, the supervisory relay 29 not being' energized to cause the attraction of its armature 34. The operatorA manipulates her listening-hey and ascertains the number of the substation with which the calling subscriber desires connection. Learning that the substation B is desired, the operator applies the tip-contact of her calling-plug 22 to one of the test-thimbles 18 of the line-jacks associated with the telephoneline to substation B. If this line isv not in use and the armature 15 of the differential cut-olf relay is consequently not attracted, the test-thimbles will be insulatedi'rom other parts of the telephone system, and the application of the test-contact of a calling-plug' will cause no change in the potential of the tip-strand associated therewith, nor will a closed electric circuit be established to cause a click in the operators receiver. It', on the other hand, a plug,` of some other cord-circuit has already been inserted within a Jack asso- IOO IIO

IIS'

the difference in potential between the testcontact and the test-thimble is made comparatively small. In the system herein described the potential ot' the test-thimble ot a busy line on which the receiver has been removed from its hook is never less than a certain limiting minimum value, depending upon the relative resistances of the relay-windings and the high-impedance windings in the circuit. The potential of the test-thimble of a busy line on which the receiver has been removed from its hook may be somewhat greater than this minimum value, an amount dependent upon the resistances in the line-circuit. Yith metallic lines of ordinary length this limiting minimum value ot' the potential ot' the testthimble of a busy line is never very greatly exceeded. In accordance with my invention I provide means whereby the potential ot' the test-contact before making a test connection is charged to a potential preferably slightly lower than the limiting minimum value of the potential of the test-thimble ot` a busy line on which the receiver has been removed from its hook. In practice I have found it desirable where the limiting minimum potential ot the test-thimble is twenty volts above that of the earth to make the `potential of the testing-contact approximately eighteen or nineteen volts. rIhis may be accomplished by connecting the conductor 43 to an element 45 ot the battery l() eighteen or nineteen volts removed in potential from the positive grounded terminal of the battery 10.

It will be apparent that the testing system herein described may be equally well applied to other telephone-exchange systems, and I do not, therefore, wish to limit myselfI to the precise disclosure herein set forth; but,

Having described my invention, I claim as new and desire to secure by Letters Patent- 1. In a telephone-exchange systern,the combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange for supplying talking and signaling' currents to said line, a test-thimble normally disconnected from said source, cord connecting apparatus at the exchange for connecting' said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line causes connection of said test-thimble with said source, a test-contact connected to a point in said source of current intermediate in potential between the potentials of the terminals of said source of current, and a signal-receiving device adapted upon application of the charged test-contact to the testthimble, to indicate the condition of the tested line.

2. In a telephone-exchange system,thc combination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at theexchange tor supplying talking` and signaling currents to said line,

a testthimble normally disconnected Vfrom said source, cord connecting apparatus at the exchange for connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line causes connection ot' said test-thimble with said source, a test-contact associated with said cord connecting apparatus,connected to a point in said source of current intermediate in potential between the potentials of the terminals ot' said source of current, and an operator-s telephone set inductively associated with the test-circuit,whereby a click is produced in the operator-s receiver, upon the application of the charged test-contact to the test-thimble of a busy line.

3. Inatelephone-exchange system, the couibination with a telephone-line extending by its limbs from a substation to an exchange, of a source of current at the exchange for supplying talking and signaling currents to said line, a test-thimble normally disconnected from said source, cord connecting apparatus at the exchange for connecting said line with another for conversation, means whereby the connection oi' said cord connecting apparatus with said line causes connection of said testthimble with said source, a test-contact connected to such a point in said source of current intermediate in potential between the potentials ot the terminals ot said source of current that the test-contact is charged to a potential only slightly diiferent from the potential of the test-thimble of a busy line, and a signaling device adapted, upon application of the charged test-contact to the test-thimble, to indicate the condition of the tested line.

a. In a telephone-exchange system, the combination with a telephone-line extending by its limbs from a substation to an exchange, of a common battery at the exchange for supplying talking and signaling currents to said line, cord connecting apparatus at the exchange for connecting said line with another for coversation, a test-thimble normally disconnected from said battery, means whereby the connection ot' said cord connecting apparatus with said line having a conductively-completed circuit through a substation-transmitter causes said test-thimble to be connected with said battery and charged to a potential intermediate between the potentials of the terminals of said common battery, a test-contact forming the tip-contact of the calling-plug associated with said cord connecting apparatus connected through an impedance-coil, to an intermediate element in said common battery such that the test-contact will be charged to a potential only slightly different from the potential of the test-thimble of a busy line, and an operators telephone set inductively associated with the test-circuit, whereby a click is produced in the operators receiver upon the application of the charged test-contact to the test-thimble of a busy line.

lof

lfnatelephone-exchange system, the combina-tion with a telrmhoned ine extending by its limbs trom a substation to an exchange, ol a source ot' current at the exchange for supplying talkingand signalingcurrents to said line, a plurality of test-thimbles YI'or said line normally disconnected from circuit, cord conuecting apparatus at the exchange for connecting said line with another tor conversation, means whereby the connection ot said cord connecting apparatus with said line causes said testthimblcs to become charged by said source, a test-contact adapted to be connected to a point in said 4source ol" current intermediate in potcntial between the potentials oi" the terminals oi said source, and a signal-receiving device adapted upon application ol the charged testcontact to a charged test-thimble to indicate the condition oi the tested line.

lj. .l n a telephone-exch ange system, the combination with a telephone-line extending by its limbs 'from a substation to an exchange, of a source ot current at the exchange for supplying talking' and signaling' current to said line, a plurality otl test-thimbles tor each line normally disconnected from circuit, a cord-circuit at the exchange for connecting' said line with another Vtor conversation, means whereby the connection ol. said cord-circuit with said line causes said test thiinbles to be charged by said source, a test-contact il'or said cord-circuit, an operators listening-key for said cord-circuit, actuation ol'l said key causing said test-contact to be connected to an intermediate point in said source, and an operators telephone set connected in circuit upon actuation of said key for receiving the signal upon application o1 the charg'ed test-contact to a charged test-thimble.

T. lin atelephone-exchange system, the combi nation with a telephone-line extending` by its limbs trom a substation to au exchange, of a source ot' current at the exchange for su pplying talking' and signalingcurrents to said line, a plurality o'l,E test-thimbles for said line nor mally disconnected from circuit, a cord-cir cuit at the exchange ior connecting said line with another for conversation, i'neans whereby the connection of said cord connecting' apparatus with said line causes said test-third bles to be charged by said source, a test-eontact For said cord-circuit normally connected with a terminal ol said source, an operators listeningkey, actuation ot said listening-key serving to disconnect said test-contact :trom 'the terminal otl said source and to connect said contact with an intermediate point ol3 said Isource to charge the teslrthimble to a slightl y ttt ditlierent potential lrom thecharged test-thimbles, and an operato1"s telephone set adapted tor connection in circuit upon actuation el said key YFor rccei.'ing the signal upon application of the charged test-contact to a charged test-th imble.

8. .ln a telephoneexchange system, the coinbination with a telrmhone-line extending' by its limbs Afrom a substation to an exchange, oi' a source oil current at the exchange, a testthilnble for said line normally disconnected from circuit, a cord-circuit at the exchange for connecting said line with another 'for conversation, means whereby the connection ol said cord connecting' apparatus with said line causes said test-thimble to he charged from said source, a test-contact ior said cord-circuit norn'ially disconnected from but adapted to he connected to an intern'iediate point ot' said source to be charged toa potelitial slightly diiii'erent 'from the potential oli the charged test-thin'rble, and sigmtl-receiving means lor indicating the condition oi the tested line upon application of a charged test-contact to the test-thimble.

9. ln a telepl1onecxchange system, the co1nbination with a telephone-line extemling by its limbs trom a substation to an exchange, ot a source oi current at the exchange for supplying talking and signalingcurrents to said line, cord connecting apparatus at the exch ange :ter connecting said line with another tor conversation, a test-thimble normally disconnected 'from said line, but adapted upon the connection oi said cord connecting' apparatus with said line to be connected with said line, means whereby the connection et said cord connecting ap] aratus with a line having a conducir iVely-eompleted circuit through a substatioutransmitter, causes said test-thiinble to be charged to a potential intermediate between the potentials ot' said. source of current, a testcontact associated with said cord connecting apparatus, means tor charging said test-contact to a potential intermediate between the potentials ol the terminals oit said source of current but dii'l'erent from the potential ot the test-thiinble ot' a busy line, and a signaling device adapted upon zuujilieation ot the charged test-contact to the test-thiinble to indicate the condition of the tested line.

ln witness whereof .l hereunto subscri be my naine this 15th day oi' April, A. D. 1903.

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